The invention relates to pneumatic tools, and more particularly to an open ended, power driven tubing wrench wherein a rotatable drive socket must be properly aligned within its housing in order to permit access to and removal of the tool from a length of tubing. Generally, such a tool applies a desired torque to a fastener by slowing to a stall when the desired torque level is reached. The output torque of the tool is regulated through line pressure.
Earlier tubing wrenches employing a rotatable, slotted socket member had to be realigned by hand with the corresponding slot in the housing. Often a release lever was provided to disengage a portion of the drive train leading to the socket member, thereby permitting its free rotation by hand to the aligned position. Subsequently various means were suggested for providing automatic return of the socket member following the tightening of a fastener. See, for example, U.S. Pat. No. 3,535,960, assigned to the same assignee as the present application. The device of this patent utilized a spring which stored rotation energy as the tool was first actuated, then released the energy after removal of the socket member from the fastener to return the socket member to its aligned position. A yieldable detent means was provided to sense the aligned position.
U.S. Pat. No. 3,620,105 discloses an air powered return mechanism for a tubing wrench. The air supply line of the tool includes a bleed orifice which constantly admits a small volume of air to the air motor to drive it slowly in the forward direction. A mechanical detent means connected to the trigger is operable to stop the tool drive mechanism in the desired position when the trigger is released and the motor is operating only on bleed air. When the trigger is depressed, the detent means is cammed into a disengaged position. The patented tool provides an effective return, but besides requiring a mechanical trigger extension lever which is somewhat cumbersome and not adaptable to tubing wrenches which are not of the gun type, the apparatus of this patent also requires a constant bleed of air through the motor, even when the tool is not being used.